bscan: rename from bscan_spi, add TAP primitives for the SVF player

The module outgrew its "SPI bridge" name — it's mostly generic
single-device JTAG TAP primitives now. Rename modules/bscan_spi ->
modules/bscan (dir, files, library target, includes, doc paths);
bscan_* function names and bscan_spi_xfer() kept.

Add the two primitives the SVF player needs beyond shift_dr:
- bscan_shift_ir: general IR scan with TDO capture (bscan_set_ir is
  opcode-only, no readback)
- bscan_tap_reset: force Test-Logic-Reset, land in Run-Test/Idle

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

bscan_proxies/README.md

@@ -7,7 +7,7 @@ enabling fast SPI flashing — see `doc/tutorial.md`, Phase 2.5.
 These `.bit` files are **not** built here. They come from
 [quartiq/bscan_spi_bitstreams](https://github.com/quartiq/bscan_spi_bitstreams),
 © QUARTIQ GmbH, MIT-licensed — see `LICENSE.quartiq`. The host-side
-framing in `modules/bscan_spi/` matches OpenOCD's `jtagspi` so the same
+framing in `modules/bscan/` matches OpenOCD's `jtagspi` so the same
 bitstreams work.
 
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